The invention relates to a matching or adapter amplifier for an induction probe for the detection of alternating magnetic fields which are emitted by magnetic field sources disposed in water, in particular, by floating bodies. More particularly, the present invention relates to such an amplifier which comprises an operational amplifier which is configured as an isolating amplifier and a frequency response-determining network.
It is known to detect alternating magnetic fields propagating in water by means of induction probes and to draw conclusions with respect to the magnetic field source by way of suitable processing of the measuring signals produced by the induction probes. Magnetic fields of this type are generated, for example, by floating bodies, which may be, for example, a submarine or a torpedo. In the case of a submarine, such alternating magnetic fields are generated, for example, by the propelling unit, the electric motor, the corrosion currents modulated by the turn of the propeller and by data processing systems in which software programs are run with different loading cycles and which modulate the currents that flow within the data processing system. These primary alternating magnetic fields emitted by such a floating body are of low frequency and characterized by a stochastic signal character.
With the assistance of probes of this type, it is possible to detect magnetic field sources in water from a distance of several hundred meters. If at least two induction probes are used, it is then possible to obtain, from the measuring signals of both probes, distance and direction information with respect to the magnetic field source, that is, to locate the magnetic field source. For this purpose, the measuring signals that are present at the output of such induction probes must be evaluated with respect to their relationship to one another.
The measuring signal of an induction probe corresponds to the differentiation over time of the magnetic induction. During this process, the stochastic signal portions that are disposed in the covered alternating field of the magnetic induction are decorrelated. If these decorrelated signal portions are now evaluated with respect to their relationship to one another, this leads to extreme position finding errors. In order to avoid such position finding errors, it is therefore indispensable to assure the synchronous operation of the at least two induction probes with respect to their amplitude response and phase response.
Since an adapter or matching amplifier is usually also connected downstream of the probes, a synchronous operation of the adapter amplifiers is also indispensable for the evaluation of the output signals of two probes. A known adapter or matching amplifier of the type mentioned at the outset is disclosed in German Patent No. DE 26 25 964 C3 and is provided with an input stage which acts as isolating amplifier, a 16 2/3 Hz trap circuit for the suppression of interferences from the operation of electric railway locomotives, and a 10 Hz low-pass filter for the suppression of higher-frequency signal portions or components such as, e.g., of the network frequency 50 Hz. All three stages are implemented with low-noise integrated semiconductor amplifiers. An adapter or matching amplifier of this type cannot counteract the decorrelation of stochastic signal portions taking place in the induction probe.
It is the object of the invention to provide an adapter or matching amplifier of the type mentioned at the outset for induction probes for detecting, in particular, low-frequency alternating fields, with the adapter or matching amplifier amplifying the measuring signals emitted by the induction probe in such a way that these can be placed into relationship with respect to one another in the proper amplitude and phase, and that the evaluation of this relationship results in useful measuring results with a low error tolerance.